1. Field of the Invention
The present invention relates a vehicle seat for use in automobiles or airplanes and more particularly to such seat employing resin frames formed by blow molding.
2. Description of the Prior Art
It is conventionally well known to form resin hollow members by means of blow molding and methods of forming automotive seat frames integrally by the blow molding have been also proposed.
In blow molding, generally, raw resin is extruded from a head in a tube-like manner such that it hangs down vertically, and in tube-like extrusion is trimmed as necessary and is closed at its ends to form a bag configuration, which is then accomodated into a mold composed of two divided parts. This mold surrounds the entire tube-like resin to be molded except a passage for air. The air passage can be provided by a nozzle which is extended down from the head. A nozzle mounted to the bottom of the mold or a nozzle provided at the side portion of the mold is used to blow air into the resin to be molded so that the resin being molded is expanded within the closed mold. After the expanded resin or molding is cured, the closed mold is opened to stop the pressurizing treatment, that is, the blow-in of air, so that the finished hollow resin member can be taken out of the mold.
When the resin hollow member is formed in this manner, both side walls (1a),(1b) of the hollow portion (2) of the hollow member (1) have their respective thicknesses t1 and t2 which are respectively a half of the thickness 2t of the remaining portions of the hollow member as well as are equal to each other. This is because the two divided parts of the mold are formed to be equal to each other in their respective surface areas. Therefore, most of the moldings are symmetric with respect to plane.
On the other hand, as shown in FIG. 1(B), if the bisected mold is varied in surface area, then the thickness t1 of the plastic side wall (1a) which is attached to the mold part larger in surface area becomes thinner than the thickness t2 of the other side wall (1b), that is, the following relation is obtained; t1&lt;t2.
These phenomena have been considered as disadvantage in the prior art blow molding technique. However, the present invention makes positive use of such phenomena to form a hollow member, i.e., a resin seat frame.